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1
Adjust oven racks to upper third and lower third positions and preheat oven to 350u00b0F. Line 2 baking sheet with parchment paper.
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2
Toast oats in large skillet over medium-high heat, stirring occasionally, until fragrant, 6 to 8 minutes. Transfer to medium bowl. Stir in flour, Grape-Nuts, baking powder, baking soda, and salt. Set aside.
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3
Wipe out skillet. Melt butter over medium heat. Cook until browned, 6 to 8 minutes, occasionally swirling pan. The butter will foam during cooking; subsiding foam is an indicator that it's almost done. Once the solids are caramel brown remove pan from heat and immediately pour butter into a large bowl, scraping in all the solids.
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4
Whisk sugar, egg, and vanilla into brown butter. With a wooden spoon or rubber spatula, stir in oatmeal mixture. Mix until just combined. Stir in blueberries.
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5
Drop dough by heaping tablespoons on prepared baking sheets, spacing them about 2 inches apart. Flatten the dough slightly with fingertips. Bake cookies until golden, 12 to 14 minutes, alternating sheets halfway through baking.
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6
Transfer to cooling racks, and cool cookies on sheets until firm, 5 to 10 minutes. Transfer cookies directly to cooling racks and cool completely. Serve at room temperature or completely cooled.
